U.S. patent number 3,884,676 [Application Number 05/373,998] was granted by the patent office on 1975-05-20 for dispersion strengthening of metals by in-can processing.
This patent grant is currently assigned to SCM Corporation. Invention is credited to Erhard Klar, Anil V. Nadkarni.
United States Patent |
3,884,676 |
Nadkarni , et al. |
May 20, 1975 |
**Please see images for:
( Certificate of Correction ) ** |
Dispersion strengthening of metals by in-can processing
Abstract
A self-contained powder metal mixture is dispersion strengthened
within a sealed container by internal oxidation and thereafter
extruded from the same sealed container to produce
dispersion-strengthened metal stock or articles. The metal mixture
comprises a mixture of powdered alloy and oxidant for complete
internal oxidation of the alloy by the oxidant, and is adapted to
dispersion strengthen the residue of oxidant upon coalescence and
hot-working thereof in the extrusion step to produce
dispersion-strengthened metal articles directly from the same
container utilized for internal oxidation.
Inventors: |
Nadkarni; Anil V. (Baltimore,
MD), Klar; Erhard (Pikesville, MD) |
Assignee: |
SCM Corporation (New York,
NY)
|
Family
ID: |
26911995 |
Appl.
No.: |
05/373,998 |
Filed: |
June 27, 1973 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
217506 |
Jan 13, 1972 |
3779714 |
|
|
|
Current U.S.
Class: |
419/3; 75/235;
148/513; 75/234; 75/252 |
Current CPC
Class: |
C22C
32/00 (20130101); C22C 1/1078 (20130101) |
Current International
Class: |
C22C
1/10 (20060101); C22C 32/00 (20060101); B22f
001/04 () |
Field of
Search: |
;75/.5BC,206,211
;148/11.5R,11.5F ;29/182.5,191.2 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Stallard; W.
Attorney, Agent or Firm: Schmitz; Thomas M.
Parent Case Text
BACKGROUND OF THE INVENTION
This is a continuation-in-part of our copending application Ser.
No. 217,506 filed on Jan. 13, 1972, now U.S. Pat. No. 3,779,714 and
said application is incorporated herein by reference.
Claims
We claim:
1. A self-contained powder metal mixture adapted to be dispersion
strengthened by internal oxidation and extruded under heat and
pressure, the self-contained powder metal mixture comprising:
an intimate mixture of 100 weight parts of a powdered alloy and at
least about 0.1 weight parts of an oxidant, said powdered alloy
having an average particle size of less than 300 microns and
consisting of a relatively noble matrix metal having a negative
free energy of oxide formation at 25.degree.C of up to 70
kilocalories per gram atom of oxygen, and a solute metal having a
negative free energy of oxide formation exceeding the negative free
energy of oxide formation of said matrix metal by at least about 60
kilocalories per gram atom of oxygen at 25.degree.C, said oxidant
consisting of an intimate mixture of heat-reducible metal oxide
having a negative free energy of formation at 25.degree.C of up to
70 kilocalories per gram atom of oxygen, and finely divided hard,
refractory metal oxide having a negative free energy of formation
exceeding the negative free energy of formation of said
heat-reducible metal oxide by at least about 60 kilocalories per
gram atom of oxygen at 25.degree.C;
said heat-reducible metal oxide being present in substantially
stoichiometric proportion for complete oxidation of said solute
metal in said alloy whereby a residue of heat-reducible metal oxide
remains in said powder metal mixture after internal oxidation
adapted to be dispersion strengthened during coalescence by said
hard, refractory metal oxide; and
a metal container comprising side wall portions, a forward wall,
and a rearward wall, said walls defining a cavity within said metal
container for containing said powder metal mixture of alloy and
oxidant free from contamination during internal oxidation and
extrusion whereby said powder metal mixture is adapted to be
dispersion strengthened within said metal container and directly
extruded from said metal container.
2. The self-contained powder metal mixture of claim 1 wherein said
oxidant exceeds the stoichiometric proportion for complete
oxidation of said solute metal to leave reducible oxides of less
than 0.1% by weight of oxygen based on the dispersion-strengthened
metal mixture.
3. The self-contained powder metal mixture of claim 1 wherein said
walls have a wall thickness greater than one-sixteenth inch.
4. The self-contained powder metal mixture of claim 1 wherein said
container is copper and said noble matrix metal of the alloy is
copper.
5. The self-contained powder metal mixture of claim 1 wherein said
container is nickel and said noble matrix metal of the alloy is
nickel.
6. The self-contained powder metal mixture of claim 1 wherein said
container is steel and said noble matrix metal of the alloy is
iron.
7. A process for dispersion strengthening a self-contained powder
metal mixture and extruding metal stock from the same container,
comprising:
providing a metal container having a cavity therein for receiving a
powder metal mixture adapted to be dispersion strengthened, said
metal container for containing the metal mixture during internal
oxidation and extrusion;
filling said metal container with powder metal mixture comprising
about 100 weight parts of a powdered alloy and at least about 0.1
weight parts of an oxidant, said powdered alloy having an average
particle size of less than 300 microns and consisting of a
relatively noble matrix metal having a negative free energy of
oxide formation at 25.degree.C of up to 70 kilocalories per gram
atom of oxygen, and a solute metal having a negative free energy of
oxide formation exceeding the negative free energy of oxide
formation of said matrix metal by at least about 60 kilocalories
per gram atom of oxygen at 25.degree.C, said oxidant consisting of
an intimate mixture of heat-reducible metal oxide having a negative
free energy of formation at 25.degree.C of up to 70 kilocalories
per gram atom of oxygen, and finely divided hard, refractory metal
oxide having a negative free energy of formation exceeding the
negative free energy of formation of said heat-reducible metal
oxide by at least about 60 kilocalories per gram atom of oxygen at
25.degree.C, said heat-reducible metal oxide being present in
substantially stoichiometric proportion for complete oxidation of
all said solute metal in the said alloy;
heating said container at a temperature of at least about
1400.degree.F to internally oxidize said solute metal of the alloy
and form a residue of heat-reducible metal oxide whereby said alloy
is dispersion strengthened; and
extruding said dispersion-strengthened alloy from said container
under heat and pressure to thermally coalesce said internally
oxidize metal mixture and oxidant residue into
dispersion-strengthened metal stock whereby said hard, refractory
metal oxide dispersion strengthens said residue of heat-reducible
metal oxide.
8. The process of claim 7 wherein oxidant exceeds the
stoichiometric proportion required to completely oxidize said
solute metal in the alloy whereby less than 0.1% by weight of
oxygen of reducible oxides remain after the step of heating to
internally oxidize said solute metal of the alloy.
Description
Dispersion strengthening has been recognized in the past as a
method for increasing strength and hardness of metals. A solid
solution alloy comprising a relatively noble matrix metal having
relatively low heat or free energy of oxide formation and a solute
metal having relatively high negative heat or free energy of oxide
formation is heated under oxidizing conditions to preferentially
oxidize the solute metal. This technique is known in the art as in
situ internal oxidation of the solute metal to the solute metal
oxide or more simply "internal oxidation."
Dispersion-strengthened metal products, such as copper dispersion
strengthened with aluminum oxide, have many commercial and
industrial uses wherein high temperature strength properties and
high electrical and/or thermal conductivities are desired or
required in the finished product. Such commercial uses include
frictional brake parts such as linings, facings, drums, and other
machine parts for friction metal applications. Other commercial
uses include electrical contact point resistance welding
electrodes, electrodes generally, electrical switches and switch
gears, transistor assemblies, wires for solderless connections,
wires for electrical motors, and many other uses requiring good
electrical and thermal conductivities as well as improved strength
and hardness at elevated temperatures.
Several prior art processes for internal oxidation have been
suggested, such as disclosed in the Schreiner patent, U.S. Pat. No.
3,488,185; the McDonald patent, U.S. Pat. No. 3,552,954; and the
Grant patent, U.S. Pat. No. 3,179,515. The prior art processes,
however, invariably require delicate control over partial pressure
of oxygen during oxidation, or require removal of an oxidant
residue which otherwise would form defects in the
dispersion-strengthened metal.
Our copending application Ser. No. 217,506 provides a novel
solution to these prior art problems by providing for assimilation
of the oxidant residue into the dispersion-strengthened mixture
wherein the oxidant residue is dispersion strengthened during
thermal coalescence by a hard, refractory metal oxide provided in
the power mixture to be dispersion strengthened. Hence, the oxidant
residue formed during internal oxidation is not required to be
removed from the dispersion-strengthened metal mixture but is
dispersion strengthened and consolidated into the final metal
product and thereby forms an integral part of the
dispersion-strengthened metal stock.
It now has been found that a powder metal mixture of powdered alloy
and oxidant may be internally oxidized and dispersion strengthened
within a sealed container and subsequently extruded from the same
container during an extrusion process whereby the
dispersion-strengthened metal mixture remains in the sealed
container and is hot-worked and coalesced during extrusion to
produce a dispersion-strengthened metal article. Accordingly, a
major objective of this invention is to provide for internal
oxidation of a self-contained powder metal mixture disposed within
a sealed container and adapted for extrusion. The self-contained
powder metal mixture eliminates the intermediate steps of removing
the internally oxidized material from the container after internal
oxidation, pulverizing the sintered cake, and hydrogen reducing the
powder mixture if desired, which steps are generally the practice
of prior art processes. Elimination of these intermediate steps
essentially eliminates the problem of introducing impurities into
the dispersion-strengthened metal which often occurs in various
handling steps prior to coalescing and hot-working the metal
mixture into dispersion-strengthened metal stock. Contamination is
particularly detrimental to electrical conductivity.
Futher advantages of this invention include elimination of the
prior art step of pulverizing the sintered mass produced by
internal oxidation and screening.
A further advantage of this invention is the elimination of a
hydrogen reduction step required in prior art processes.
Another advantage of this invention is the elimination of a double
heat-up of the material wherein the powder mixture is first heated
to high temperatures during internal oxidation and subsequently
heated again to high temperatures prior to extruding. Both heating
processes are combined in this invention without intermediate
cooling which is more economical and substantially improves the
quality of the final dispersion-strengthened product.
Still another advantage is increased extrusion output capacity
wherein the packed density of the material in the can for extrusion
is increased about 20% over typical prior art methods.
These and other advantages will become more apparent from the
detailed description of the invention.
SUMMARY OF THE INVENTION
Briefly, this invention provides a self-contained powder metal
mixture of alloy and oxidant enclosed within a sealed container
wherein the mixture is dispersion strengthened by internal
oxidation to form a hard, sintered cake therein, and thereafter
hot-worked and coalesced by extrusion from the same sealed
container. The powder metal mixture of powdered alloy and oxidant
is intimately intermixed wherein the alloy comprises matrix metal
and solute metal and the oxidant comprises heat-reducible metal
oxide and hard, refractory metal oxide. Sufficient oxidant is
combined with the alloy in approximately stoichiometric proportions
for complete oxidation of the alloy solute metal. A residue of
heat-reducible metal oxide produced during internal oxidation
becomes dispersion strengthened during coalescence and extrusion
whereby a dispersion-strengthened metal product is produced without
removing the dispersion-strengthened metal mixture from the
container.
In the drawings:
FIG. 1 is a side elevation view of the container partially broken
away exposing a powder metal mixture therein;
FIG. 2 is an end elevation view of the rearward portion of the
container shown in FIG. 1;
FIG. 3 is a partial side elevation view of the rearward portion of
the container showing the nozzle end portion pinched; and
FIG. 4 is a block diagram indicating the processing steps of this
invention .
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the drawings wherein like numerals identify like
parts, shown is a cylindrical metal container 10 having side walls
12 of uniform thickness, a forward end wall 14, and a rearwardly
disposed end wall 16. The forward wall 14 and rear wall 16 are
secured to the side wall 12 to hermetically seal the container 10.
The rearward wall 16 is conical and protrudes outwardly from the
interior of the container 10 and is provided with a centrally
disposed nozzle 18 having an opening 20 therein. The nozzle 18 is
adapted to receive the powder metal mixture whereby the container
10 may be loaded with the powder metal mixture prior to internal
oxidation and extrusion. The nozzle opening 20 is of convenient
size relative to the size of the container 10 and, for example, may
have a diameter of about 1/2 to 1 inch. The cylindrical metal
container typically has a diameter D of 8 inches and a length L of
about 24 inches. The diameter D and/or cylinder length L may be
relatively smaller or larger depending on the size of the extruded
article, or depending on the size of the extrusion chamber of the
press. For efficiency and economy, an elongated container is
preferred whereby the cylinder length L is maximized relative to
the cylinder diameter D to minimize extrusion costs.
The overall size of the container is usually dictated by the
extrusion press available wherein the container 10 desirably has
about a 1/2 -inch clearance within the extruder feed cavity. The
forward end wall 14 of the container 10 is shown as convex although
a flat or concave forward end wall may be utilized. The side wall
thickness of the container desirably is greater than about one
sixteenth inch and preferably about one eighth inch. Larger wall
thickness may be used if desired. The forward wall 14 and the
rearward wall 16 have wall thicknesses similar to the side walls
12. The container 10 is of metal and desirably metallurgically
compatible with the alloy to be extruded. For example, a copper
container would be desirable for a copper alloy, a nickel container
would be desirable for a stainless steel or nickel alloy extrusion,
a silver container would be desirable for a silver alloy extrusion,
and a steel container is desirable for a steel extrusion.
Preferably, the metal of the container is compatible with the alloy
contained therein since the container metal itself is completely
extruded with the alloy in the extrusion process.
In practice, the container 10 is purged with inert gas such as
argon or nitrogen by introducing the same under pressure into the
nozzle 18. The powdered alloy and oxidant mixture is then
introduced into the container 10 via nozzle 18 until the container
10 is completely filled. The alloy and oxidant mixture is compacted
or settled by mechanical vibration. Thereafter the nozzle 18 is
sealed such as by welding or by pinching, as indicated in FIG. 3,
but with the provision for a small leak or pin hole 22 through the
rearwardmost portion of nozzle 18. The small leak 22 provides an
escape passage for residual gas remaining within the container 10
whereby pressure build-up is effectively avoided during subsequent
heat-up required in internal oxidation.
After the container 10 is loaded and sealed, the loaded container
10 is subjected to high heat of at least about 1400.degree.F for
internal oxidation, and desirably heated at about 1750.degree.F for
at least about one-half hour, as more particularly set forth in our
copending application Ser. No. 217,506. After the internal
oxidation step, the sealed container 10 may be placed directly into
a conventional extrusion press and extruded at temperatures of
about 1600.degree.to 1700.degree.F without prior cooling. The
extrusion step may immediately follow the internal oxidation step,
or alternatively, the container may be cooled to room temperature
and thereafter re-heated prior to extrusion. After internal
oxidation, the pin hole 22 is preferably sealed prior to extrusion
to prevent air from entering the container 10.
The foregoing self-contained powder metal mixture adapted to be
dispersion strengthened by internal oxidation in the same container
utilized for extrusion uniquely eliminates the intermediate step of
removing the internally oxidized material from the container after
internal oxidation whereby considerable expediency is achieved in
processing and the quality (purity) of the product is improved.
Referring now to the self-contained powder metal mixture disposed
within a metal container and adapted to be dispersion strengthened
and extruded from the same sealed metal container, the powder metal
mixture comprises an intimate mixture of powdered alloy of matrix
metal and solute metal and an oxidant of heat-reducible metal oxide
and hard, refractory metal oxide.
The preferred powder alloy comprises a relatively noble matrix
metal having a negative free energy of oxide formation at
25.degree.C of up to 70 kilocalories per gram atom of oxygen, and a
solute metal having a negative free energy of oxide formation
exceeding that of the relatively noble matrix metal by at least
about 60 kilocalories per gram atom of oxygen at 25.degree.C. The
preferred oxidant comprises an intimate mixture of heat-reducible
metal oxide having a negative free energy of formation at
25.degree.C of up to about 70 kilocalories per gram atom of oxygen,
and finely divided hard, refractory metal oxide having a negative
free energy of formation exceeding the negative free energy of
formation of the heat-reducible metal oxide by at least about 60
kilocalories per gram atom of oxygen at 25.degree.C. The
heat-reducible metal oxide is present in the oxidant in an amount
sufficient for complete oxidation of the solute metal in the alloy.
The hard, refractory oxide in the oxidant is present in
substantially the same equivalent elemental proportion as the
solute metal in the alloy, and both are of a particle size suitable
for dispersion strengthening of the oxidant residue resulting from
the internal oxidation, as set forth in our copening application
Ser. No. 217,506. After internal oxidation, the oxidant residue
comprises particles of in situ residue of heat-reducible metal
oxide and particles of hard, refractory metal oxide uniformly
distributed therein and the residue of heat-reducible metal oxide
is intimately dispersed within the alloy powder. The
dispersion-strengthened metal mixture is eventually coalesced and
consolidated by hot-working to form a solid metal workpiece whereby
the residue of heat-reducible metal is dispersion strengthened by
the hard, refractory metal oxide and forms an integral parts of the
dispersion-strengthened resulting workpiece.
To achieve the proper proportion of oxidant, about 0.1 to about 10
parts by weight of oxidant are employed per 100 parts of alloy to
be internally oxidized. The exact proportions depend on the solute
metal to be oxidized, the concentration of solute metal in the
alloy, and the oxygen content of the oxidant. The heat-reducible
metal oxide is present in substantially stoichiometric proportions
for internally oxidizing all of the solute metal in the alloy. At
least about 0.1 weight parts of oxidant are combined per 100 weight
parts of powder alloy, desirably between about 0.1 to 20 weight
parts of oxidant, and preferably about 0.1 to 10 weight parts of
oxidant are combined with about 100 weight parts of powder alloy.
Preferably, the proportion of the heat-reducible metal oxide and
the hard, refractory metal oxide is predetermined so that the
composition of the oxidant residue and internally oxidized alloy
are substantially identical in the dispersion-strengthened metal
after the internal oxidation step is completed. The amounts of such
oxidants to be added may be determined by the stoichiometric amount
of oxygen required to oxidize the solute metal completely, but
preferably excessive amounts of oxidant are not used so as to avoid
leaving more than about 0.1% of reducible oxygen in the internally
oxidized metal mixture.
Thus, the internally oxidized metal mixture would not lose greater
than about 0.1% by weight after subjecting the same to a hydrogen
reduction test. The hydrogen reduction test may be applied to a
representative sample of internally oxidized metal mixture by
removing the same from the sealed container after the internal
oxidation step is completed. The sintered mass is then pulverized,
screened, weighed, and then subjected to a hydrogen atmosphere at a
temperature of 1600.degree.F for one half hour. The measured weight
loss preferably is no greater than about 0.1% based on the total
sample tested.
In practicing this invention, the powdered alloy comprising a
relatively noble matrix metal and a solute metal is produced by
conventional techniques such as melting the metal under inert or
reducing conditions and thereafter comminuting the alloy by
atomization or other conventional size-reduction techniques such as
grinding or ball milling to form a particulate alloy having an
average particle size of less than about 300 microns.
The noble matrix metal in the alloy and the in situ, heat-reduced
metal in the oxidant residue are defined broadly as those metals
having a melting point of at least about 200.degree.C and whose
oxides have a negative free energy of formation at 25.degree.C of
from 0 to 70 kilocalories per gram atom of oxygen. Suitable alloy
matrix metals and corresponding heat-reducible metal oxides for
practicing the present invention include the following: iron (FeO,
Fe.sub.2 O.sub.3); cobalt (CoO); nickel (NiO); copper (Cu.sub.2 O,
CuO); cadmium (CdO); thallium (Il.sub.2 O); germanium (GeO.sub.2);
tin (SnO, SnO.sub.2); lead (PbO); antimony (Sb.sub.2 O.sub.3);
bismuth (Bi.sub.2 O.sub.3); molybdenum (MoO.sub.2,MoO.sub.3);
tungsten (WO.sub.2, WO.sub.3); rhenium (ReO.sub.3); indium
(In.sub.2 O.sub.3); palladium (PdO); osmium (OsO.sub.4); platinum
(PtO); and rhodium (Rh.sub.2 O.sub.3) as more particularly set
forth in our copending application Ser. No. 217,506.
In any particular combination of matrix metal and solute metal in
the alloy to be dispersion strengthened by internal oxidation, the
matrix metal must be relatively noble with respect to the solute
metal so that the solute metal will be preferentially oxidized.
This is achieved by selecting the solute metal such that its
negative free energy of oxide formation at 25.degree.C is at least
60 kilocalories per gram atom of oxygen greater than the negative
free energy of formation of the oxide of the matrix metal at
25.degree.C. Such solute metals have a negative free energy of
oxide formation per gram atom of oxygen of over 80 kilocalories and
generally over 120 kilocalories. Suitable alloy solute metals and
corresponding hard, refractory metal oxides include: silicon
(SiO.sub.2); titanium (TiO.sub.2); zirconium (ZrO.sub.2); aluminum
(A1.sub.2 O.sub.3); beryllium (BeO); thorium Th0.sub.2); chromium
(Cr.sub.2 0.sub.3); magnesium (Mg0); manganese (Mn0); niobium
(Nb.sub.2 0.sub.5); tantalum (Ta.sub.2 0.sub.5); and vanadium (VO),
as more particularly set forth in our said copending application
Ser. No. 217,506.
The metal moiety of the heat-reducible metal oxide in the oxidant
preferably is the same metal as the matrix metal present in the
alloy to be internally oxidized, although the heat-reducible metal
oxide moiety can be different. For instance, alloy matrix
metal/oxidant heat-reducible metal oxide combinations include:
ALLOY MATRIX OXIDANT HEAT-REDUCIBLE METAL METAL OXIDE
______________________________________ copper cobalt oxide, nickel
oxide, copper oxide nickel cobalt oxide, nickel oxide, copper oxide
cobalt cobalt oxide, nickel oxide, copper oxide
______________________________________
Similarly, the hard, refractory metal oxide in the oxidant
preferably is the same as the solute metal oxide formed in the
alloy during internal oxidation of the alloy, although the
refractory metal oxide in the oxidant can be different from the
solute metal oxide in the internally oxidized alloy. For example,
solute metal oxide/oxidant hard, refractory metal oxide
combinations include:
ALLOY SOLUTE OXIDANT HARD, REFRACTORY METAL OXIDE METAL OXIDE
______________________________________ Al.sub.2 O.sub.3 Al.sub.2
O.sub.3, BeO, ZrO.sub.2, ThO.sub.2 BeO Al.sub.2 O.sub.3, BeO,
ZrO.sub.2, ThO.sub.2 ZrO.sub.2 Al.sub.2 O.sub.3, BeO, ZrO.sub.2,
ThO.sub.2 ThO.sub.2 Al.sub.2 O.sub.3, BeO, ZrO.sub.2, ThO.sub.2
______________________________________
In accordance with this invention, the stoichiometrically
porportioned alloy and oxidant are contained within a sealed
container preparatory to the internal oxidation step. The container
must be adaptable for both high temperature internal oxidation and
subsequent high temperature extrusion.
The following illustrative examples are included to further explain
the invention and are not intended to be limiting. All parts are by
weight and all temperatures are in degrees Fahrenheit, unless
otherwise stated.
EXAMPLE 1
Part A -- Preparation of the Alloy Powder
Electrolytic tough-pitch grade copper rods were melted in an inert
refractory crucible in an induction heating furnace under reducing
conditions at a temperature of about 2300.degree.F. Metallic
aluminum shavings were introduced into the molten copper in the
proportion of 0.33% by weight of the resulting molten metallic
mass.
The molten solution of aluminum in copper was then super-heated to
2400.degree.F, atomized through an atomizing aperture in a jet of
nitrogen to yield an atomized copper-aluminum alloy powder which
substantially all passed a 100-mesh U.S. Sieve indicating that the
average particle size was less than about 140 microns.
Part B -- Preparation of the Oxidant
One hundred parts of commercially available cuprous oxide (Cu.sub.2
0) with an average particle size of about 1 to 2 microns were mixed
with 4.1 parts of A1(NO.sub.3).sub.3 . 9H.sub.2 0 dissolved in
water to form a slurry of cuprous oxide in aluminum nitrate
solution. The solution of aluminum nitrate was slurried with
cuprous oxide particles, and stirring was continued with mild
heating at 200.degree.F until the water had evaporated and the
mixture had become almost dry. The mixture was then heated at a
temperature of about 500.degree.F for one-half hour to decompose
the aluminum nitrate into aluminum oxide. The resulting agglomerate
was then ground to form fine oxidant powder which passed a 325-mesh
sieve. The resulting oxidant powder comprised 77.43% Cu.sub.2 0,
and 0.56% A1.sub.2 0.sub.3 by weight.
Part C -- Preparation of Powder Metal Mixture
The alloy powder of Part A was thoroughly mixed with the oxidant
powder to Part B in the proportion of 2.12 parts of oxidant to 100
parts of alloy powder to provide a powder mixture of alloy and
oxidant. Mixing was achieved in a ball-mill.
Part D -- Internal Oxidation
The alloy powder-oxidant mixture of Part C was then charged into an
internal oxidation vessel. The oxidation vessel was a cylindrical
copper container having an overall length of 24 inches, a diameter
of 8 inches, and a wall thickness of one-eighth inch. Approximately
234 pounds of the foregoing alloy-oxidant powder mixture were
charged into the container, purged with argon gas, and thereafter
sealed leaving a pin hole opening for pressure release.
The alloy oxidant powder mixture was then brought to a temperature
of about 1750.degree.F and maintained at this temperature for about
30 minutes to effect internal oxidation of the alloy powder.
At the end of the 30-minute internal oxidation period,
substantially all of the aluminum in the alloy powder was oxidized
to Al.sub.2 O.sub.3 and substantially all of the cuprous oxide in
the oxidant had been reduced to metallic copper. The particles of
internally oxidized alloy comprises 99.37% by weight of copper plus
negligible amounts of impurities and 0.63% by weight of Al.sub.2
O.sub.3 and the oxidant residue comprised 99.37% copper particles
and 0.63% Al.sub.2 O.sub.3 particles. The overall internally
oxidized metal powder composition comprised 98.21% internally
oxidized alloy powder and 1.79% oxidant residue.
Part E -- Thermal Coalescence and Extrusion
The container of internally oxidized metal mixture was then placed
in a ram-type extrusion press and was extruded to form extrudate in
the shape of cylindrical bar stock having a diameter of about 1.125
inches. This corresponds to an extrusion ratio of about 50:1 (i.e.,
the ratio of the cross-sectional area of the can to the
cross-sectional area of the extrudate).
The bar stock was about 99.37% copper having dispersed throughout
0.63% (or about 1.5% by volume) of Al.sub.2 O.sub.3 particles. The
bar stock had a density of about 99.3% of the theoretical density,
an electrical conductivity of 88% IACS, a tensile strength of about
72,000 psi, an elongation of 19% using ASTM Test E-8 (for a test
specimen 0.16 inch in diameter and 0.65 inch gage length) and a
Rockwell hardness of about 75 units on the B scale. All property
measurements were made at room temperature.
A sample of the bar stock was reduced by 50% in cross-sectional
area by cold swaging whereby the tensile strength became 80,000
psi, the elongation 13% Rockwell B hardness 84 units, and
conductivity 86% IACS.
EXAMPLE 2
The procedures of Example 1 were repeated except that the 8-inch
diameter copper can was replaced by a 1.25-inch diameter copper
can. The extrusion was carried out in an extrusion chamber of
1.38-inch diameter at an extrusion ratio of 30:1 yielding a
0.250-inch diameter rod. Such rod had an electrical conductivity of
86.7% IACS, a tensile strength of about 73,000 psi, and an
elongation of 19.8% in a gage length of 0.650 inch.
EXAMPLE 3
The material of Part D of Example 1 was fed into a thin-walled
copper can of 1.25-inch diameter and extruded in an extrusion
chamber of 1.38-inch diameter at an extrusion ratio of 45:1 to
yield a rod of 0.206-inch diameter. This rod had an electrical
conductivity of 89% IACS. The rod was swaged and drawn to a
0.010-inch diameter wire and heat treated at 500.degree.C for
one-half hour in helium and produced an ultimate tensile strength
of 84,000 psi, a yield strength of 71,200 psi, and an elongation of
about 5% in 10 inches
EXAMPLE 4
Dispersion-strengthened metal bar stock is formed by the
above-described method by oxidizing 100 parts of a powdered alloy
of 98.86% nickel and 1.14% aluminum with 4.76 parts of pulverulent
oxidant comprising 4.68 parts of nickel oxide and 0.08 parts of
aluminum oxide. In this example, a nickel metal container is
utilized for internal oxidation and subsequent extrusion. The
resulting dispersion-strengthened bar stock has increased tensile
strength and hardness at elevated temperatures relative to bar
stock of a similar nickel-aluminum alloy which has not been
internally oxidized.
EXAMPLE 5
Dispersion-strengthened metal bar stock is formed as indicated in
Example 1 by oxidizing 100 parts of a powdered alloy of 98.72% iron
and 1.28% aluminum with 3.865 parts of pulverulent oxidant
comprising 3.800 parts of iron oxide and 0.065 parts of aluminum
oxide, but with the provision that a steel container is utilized
for internal oxidation and extrusion. The resulting
dispersion-strengthened bar stock has increased tensile strength
and hardness at elevated temperatures or after annealing as
compared relative to bar stock of a similar iron-aluminum alloy
which had not been internally oxidized.
* * * * *